check tool_returns

[sonichi]

Why are these changes needed?

Need to check whether tool_returns is empty before returning.
TODO in a separate PR: add a test to cover human_input_mode="ALWAYS"

Related issue number

Close #1174

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (2ca8aae) 30.41% compared to head (6334cf8) 39.50%.

Files	Patch %	Lines
autogen/agentchat/conversable_agent.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1187      +/-   ##
==========================================
+ Coverage   30.41%   39.50%   +9.09%     
==========================================
  Files          32       32              
  Lines        4301     4303       +2     
  Branches      993     1045      +52     
==========================================
+ Hits         1308     1700     +392     
+ Misses       2899     2477     -422     
- Partials       94      126      +32     

Flag	Coverage Δ
unittests	39.43% <25.00%> (+9.07%)	⬆️

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[ekzhu]

Are this and #1182 both required to close the bug #1174 ?

[sonichi]

Are this and #1182 both required to close the bug #1174 ?

I think so. They cover different cases. Similar to this PR, a test should be added to cover the case in #1182.

[yenif]

ah, yup thats it